If you are traveling to the island of Yap in the Federated States of Micronesia, you might consider using a credit card, rather than having to convert your cash into local currency.
The legal tender currency is called Rai, and it consists of doughnut-shaped stones, ranging from 3.5 cm (1.4 in) to 4 meters (12 feet) in diameter. The largest coins require twenty grown men to carry them.
While the US dollar is now the generally-accepted currency, the Rai continue to be honored as legal tender, although their primary purpose tends to be for traditional or ceremonial transactions.
In 1929 the inventory of official Rai amounted to 13,821 stones on the island. About half of these remain. Their value is determined by their size, and they can be converted into foreign currency through the Bank of Hawaii. A 2.5 cm (1 in) Rai is worth $72 US, and a 25 cm (10 in) Rai would fetch about $6,000 US.